In order to build a geometric model of an object's surface, range sensors have been developed. These sensors measure the distance between the sensor and the surface at a collection of points. For close range measurements, triangulation-based laser range sensors are typically used. Then, the partial or whole surface shape of an object can be modeled from measurements collected from a plurality of viewpoints. For that purpose, the relative positions between the sensor and the object should be determined before integrating the range measurements into a common global coordinate system. One can use an external positioning device or integrate auto-referencing within the sensing device. For instance, in International Patent Application published under no. WO 2006/094409A1, P. Hébert et al., describe an auto-referenced hand-held range sensor integrating a laser pattern projector and two cameras that simultaneously capture the image of the laser pattern and that of retro-reflective target features. These retro-reflective features are used for the auto-referencing and are illuminated using LEDs whose spectral band matches with the spectral band of the laser pattern projector. Based on the observation of these features, the system combines laser triangulation with the principles of photogrammetry for auto-referencing.
Compact for hand-held operations, the system builds incrementally and simultaneously a model of the 3D position of the target features for matching and calculating the current position of the range sensor while reconstructing the geometry of the surface.
Using such a system does not allow one to capture the color texture of the object's surface. One could first build the 3D model of the object's surface, and then use a color camera to collect images of the object's surface that could be aligned with the model before merging and integrating them into a textured model representation. However, such an approach would require two systems without providing a capability of building a complete model incrementally while scanning.
Another limitation of known systems is related to the resolution of the recovered model. Since the cameras are used for positioning, a wide field of view is required. Conversely, for recovering higher resolution of an object's surface shape, namely its geometry, a smaller surface section should map to a larger number of pixels in the images. Consequently, there is a compromise between positioning and the recovered resolution of the geometry.